Abstract: A message generated at a sender device is received at a messaging server via a network. The message is transmitted to a recipient device, where it is displayed in a modified format at least partly obscuring content of the message. A command is received from the sender device to unsend the transmitted message after transmitting the message to the recipient device. The messaging server determines whether the message has been displayed in an unobscured form at the recipient device, and, responsive to the message not having been displayed in the unobscured form at the recipient device, transmits a command to the recipient device to delete the message at the recipient device.